Obstructive Sleep Apnea (OSA) is a sleep-related breathing disorder that is growing in prevalence and is associated with negative cardiovascular consequences and adverse events from excessive daytime sleepiness. Insomnia is a frequently co-occurring sleep disorder that adds significant morbidity and is a potential barrier to adherence of OSA treatment. It is currently unknown if directly treating insomnia can enhance outcomes of OSA treatment. The purpose of this project is to determine the efficacy of a multidisciplinary treatment model for patients with OSA and comorbid insomnia. At the Rush Sleep Disorders Center, we have developed an approach that combines cognitive-behavior therapy (CBT) for insomnia delivered by a psychologist with Continuous Positive Airway Pressure (CPAP) therapy managed by a physician. Building upon preliminary data collected in our clinic, we seek to test the efficacy and mechanisms of this multidisciplinary model against the standard practice of treating OSA using CPAP alone. The specific aims are: 1) to determine the efficacy of a treatment model combining CBT and CPAP for individuals with OSA and comorbid insomnia; 2) to determine if there are relative benefits in the sequence of treatment initiation; and 3) to examine the mechanisms between insomnia symptoms and CPAP adherence. To carry out these aims, a three-arm randomized controlled trial will be used to compare three treatment models: A) CBT followed by CPAP; B) CBT and CPAP concurrently; and C) CPAP alone. The desired outcome of this project is to identify the optimal treatment model and to determine if there is a causal link between insomnia symptoms and CPAP adherence.